In the present specification, the term electronic device is defined as a device which does not necessarily include input/output terminals suitable for electrically connecting the device to a substrate. Examples of electronic devices include silicon or GaAs FETs, PIN diodes, silicon or GaAs IC die, acoustic devices such as surface acoustic wave (SAW) or bulk acoustic wave (BAW) resonators or filters, passive devices such as capacitors, inductors and resistors, which are fabricated in or on, for example, multi-layer low temperature co-fired ceramic (LTCC) substrates.
The term electronic component is defined as a component which includes input/output terminals suitable for connecting the component to a substrate, for example a printed circuit board (PCB) using connection techniques such as re-flow soldering. Examples of electronic components include packaged electronic devices, where the package includes terminals for connecting the component to the substrate, as well as multi-layer electronic components which include solder terminals.
Conventional discrete electronic components include an internal electronic device connected to metal input/output terminals located somewhere on the outer surface of the electronic component. Typically, the internal electronic device is housed in an outer enclosure or package, which includes the metal input/output terminals suitable for re-flow soldering. The input/output terminals of the outer enclosure are connected to input/output terminals of the internal device by one or more connectors.
One category of electronic component comprises input/output terminals which are located exclusively on the underside of the component; this type of electronic component usually employs metal-plated through holes, which run vertically through the outer enclosure of the component and which electrically connect the underside terminals of the component to internal device terminals or to internal pads which are connected to the device terminals by bond wires.
Another category of electronic component comprises input/output terminals which are partially or wholly located on the sides of the component—hereinafter referred to as side terminations. Such electronic components typically comprise one or more insulating substrate layers where electrical connections between the side terminations of the electronic component to the input/output terminals of the internal device are achieved by metal traces which are fabricated on one or more surfaces of the substrate layers of the electronic component. U.S. Pat. No. 5,428,885, Takaya describes in detail an electronic component comprising side terminations wherein a connector is employed to connect an internal electronic device of the electronic component to the side terminations of the electronic component. The connector by which the internal electronic device is connected to metal input/output terminals of an electronic component is referred to hereinafter as an electrical transition.
In RF including microwave applications, an electronic component is usually mounted on a substrate which includes a pattern of metal microstrip transmission lines or coplanar waveguide transmission lines. Each transmission line originates at a connection pad which is connected to one of the component input/output terminals and terminates at a remote location on the substrate. These metal transmission lines electrically connect the component to some other circuitry mounted on or connected to the substrate. The use of suitable transmission lines on the substrate (for example microstrip transmission lines with a characteristic impedance of 50 Ohms) ensures that the optimum electrical properties of the component are available at the remote location on the substrate where the transmission line terminates.
When an electrical component is required to operate at RF including microwave frequencies, the electrical characteristics of the electrical transition between the input/output of the component and the input/output of the internal device affect the electrical characteristics of the component. Ideally the electrical transition from the connection pad on the carrier substrate, which is connected to the input/output terminal of the component, to the input/output of the internal device should not introduce any electrical discontinuity in the path between the connection pad on the carrier substrate and the input/output of the internal device.
The description of side terminations in U.S. Pat. No. 5,428,885 takes no account of the requirement that the transitions from the connection pads on the carrier substrate to the inputs/outputs of the internal device should not introduce a discontinuity. A poor choice of transition can give rise to dissipative and mismatch losses, particularly at high frequencies of operation of the component or where the height of the side termination is comparable to one quarter of the wavelength of the input and output signals of the electronic component.
It is advantageous if the transition from the connection pad to the input/output terminal of the internal device is designed so that this transition effectively extends the transmission line on the carrier substrate of the electronic component from the connection pad on the substrate to the input/output of the internal device of the electronic component thereby eliminating any discontinuity in the signal path.
U.S. Pat. No. 6,624,521, Staiculescu relates to flip chip design on a coplanar waveguide with a pseudo-coaxial ground bump configuration. Staiculescu describes an RF coaxial transition comprising an annulus of solder balls which surround a central solder ball for the connection of a terminal of a flip-chip device to a pad at the end of a transmission line on a carrier substrate. The diameter of the annulus of solder balls and the dimensions of the solder balls are chosen so that the transition has the characteristics of a coaxial transmission line.
The RF coaxial transition described in U.S. Pat. No. 6,624,521 addresses some of the problems resulting from the discontinuity introduced by a typical electrical transition for an RF electronic component; however, it has a number of limitations. The electrical transition described in U.S. Pat. No. 6,624,521 does not provide a solution for the connection of an electronic component to a carrier substrate where the connection is achieved by re-flow soldering or in cases where the connection from the solder pad at the end of the transmission line on the carrier substrate to the internal device of the electronic component is achieved by side terminations. Furthermore the transition described in U.S. Pat. No. 6,624,521 does not provide a solution for the case when the electronic component has terminals which are connected by an internal connector to an internal device of the component as described above.